Skin acts as a natural barrier between internal and external environments and therefore plays an important role in vital biological functions such as protection against mechanical and chemical injury, micro-organisms, and ultraviolet damage. The health and appearance of skin, however, can deteriorate due to environmental factors, genetic makeup, nutrition, and sun exposure. With aging, the outer skin layer (epidermis) thins, even though the number of cell layers remains unchanged. The number of pigment-containing cells (melanocytes), however, decreases. Therefore, the skin appears pale and translucent. Large pigmented spots (age spots, liver spots, or lentigos) may appear in sun-exposed areas. Changes in the connective tissue reduce the skin's strength and elasticity. This is known as elastosis. It is more noticeable in sun-exposed areas (solar elastosis). Elastosis produces the leathery, weather-beaten appearance common to farmers, sailors, and others who spend a large amount of time outdoors. Dehydration increases the risk of skin injury. Poor nutrition can also negatively impact the skin, causing dryness, rash, and puffiness.
Ceramides are a group of natural waxy, fatty substances in the skin, composed of sphingosine and lipids (fatty acids) bonded together. Ceramides make up about 50% of all skin lipids and are manufactured in the lower, living cells of the epidermis. As the cells mature and move to the surface, ceramides are released to the topmost layer, the stratum corneum. In the stratum corneum layer, ceramides combine with cholesterol (another important lipid found in the skin) and fatty acids to form an ordered, tightly-packed, layered, sheet-like arrangement between the dead cells. Ceramides and cholesterol protect against moisture loss to keep skin youthful and supple, and support the skin's matrix, keeping it firm. Young individuals manufacture ample ceramides and cholesterol to keep the skin healthy. However, with age, production declines, and skin begins to sag and wrinkle.